Mycology Practice Questions

Q: Which of the following organisms is most likely responsible for this finding?

Candida albicans. ***Candida albicans*** - This organism is a common cause of **esophagitis** in immunocompromised patients, such as those with HIV or hematologic malignancies, often presenting with **white plaques (thrush)**. - Diagnosis is typically confirmed via endoscopy, which reveals **pseudomembranes** that can be scraped off, with biopsy showing **pseudohyphae** and **yeast cells**. *Aspergillus fumigatus* - Primarily causes **pulmonary disease**, such as **allergic bronchopulmonary aspergillosis (ABPA)** or **invasive aspergillosis** in neutropenic patients. - Histologically defined by **septate hyphae** with **acute-angle (45-degree) branching**. *Cryptococcus neoformans* - Primarily associated with **meningitis** in immunocompromised individuals, often presenting with subacute headache and altered mental status. - Typically identified by **india ink staining** of cerebrospinal fluid (CSF), showing **encapsulated yeast** with a **halo effect**. *Mucor species* - A highly aggressive fungal infection (mucormycosis) most commonly seen in patients with **diabetic ketoacidosis (DKA)**. - Characterized by **aseptate hyphae** with **wide-angle (90-degree) branching** and angioinvasion leading to tissue necrosis.

Q: A diabetic patient presents with facial pain, black nasal eschar and eye pain following corticosteroid therapy. What is the etiological agent?

Rhizopus. ***Rhizopus*** - This species belongs to the order Mucorales, the primary causative agents of **rhinocerebral mucormycosis** in immunocompromised hosts, especially in patients with **diabetic ketoacidosis**. - The clinical presentation of **facial pain**, **black nasal eschar** (due to tissue necrosis/infarction), and **eye pain** (orbital involvement) is the classic hallmark of this invasive fungal infection. *Candida tropicalis* - Typically causes **candidemia** or disseminated candidiasis in immunocompromised patients, but it does not classically present with necrotic nasal eschars. - It is a yeast, whereas the cause of this patient's condition is an **angioinvasive mold**. *Aspergillus fumigatus* - While it can cause sinusitis in immunocompromised patients, it typically presents with **allergic fungal sinusitis** or invasive disease without the classic black eschar. - It is characterized by **septate hyphae** with acute angle branching, differing from the broad, non-septate hyphae of Mucorales. *Cryptococcus neoformans* - Usually presents as **meningoencephalitis** or pulmonary infection, particularly in patients with advanced HIV/AIDS. - It is an encapsulated yeast and does not cause the rapid, destructive tissue necrosis associated with **black eschar** formation in the sinuses.

Q: A patient presents with fever, headache, and neck stiffness suggestive of meningitis. CSF examination is performed, and Nigrosin stain reveals encapsulated budding yeast cells. Which of the following organisms is the most likely causative agent?

Cryptococcus neoformans. ***Cryptococcus neoformans*** - This organism is characterized as an **encapsulated budding yeast** that is classically identified in **cerebrospinal fluid (CSF)** using **India ink** or **Nigrosin stain**. - It is the most common cause of fungal meningitis, particularly in **immunocompromised patients** (e.g., those with AIDS), and the capsule appears as a clear halo against the dark background of the stain. *Aspergillus fumigatus* - This is a **mold** that typically presents as **septate hyphae** with acute-angle (45-degree) branching, not as budding yeast. - While it can invade the central nervous system, it usually causes **abscesses** or **vascular invasion** rather than the typical yeast-like presentation in CSF. *Pneumocystis jirovecii* - This organism is an **atypical fungus** that does not grow in culture and is typically identified in lung tissue or bronchoalveolar lavage fluid using **Methenamine silver stain**. - It classically causes **interstitial pneumonia** in immunocompromised hosts and does not typically infect the meninges as a budding yeast. *Histoplasma capsulatum* - This is a **dimorphic fungus** that exists as small, intracellular yeast forms within **macrophages** in host tissues. - It is typically identified via biopsy or antigen testing, not as an encapsulated yeast in the CSF, and usually presents with systemic symptoms like hepatosplenomegaly or pulmonary involvement.

Q: Which statement is false regarding Cryptococcus neoformans?

Urease negative. **Explanation:** *Cryptococcus neoformans* is an encapsulated yeast primarily associated with pigeon droppings and is a significant opportunistic pathogen in immunocompromised patients (e.g., HIV/AIDS). **1. Why "Urease negative" is the False Statement:** *Cryptococcus neoformans* is characteristically **Urease positive**. The production of the urease enzyme is a key biochemical marker used in the laboratory to differentiate it from other yeasts like *Candida albicans* (which is urease negative). It hydrolyzes urea to produce ammonia, raising the pH and changing the indicator color. **2. Analysis of Other Options:** * **Option A (Grows at 5°C and 37°C):** This is true. Unlike many other pathogenic fungi, *C. neoformans* can grow at 37°C (essential for human pathogenicity) and also at lower temperatures like 4°C–5°C. * **Option B (Has 4 serotypes):** This is true. Based on capsular polysaccharide antigens, it is classified into four serotypes: **A, B, C, and D**. (Note: Serotype A is *C. neoformans var. grubii*, while B and C are now often classified as *C. gattii*). * **Option D (Causes superficial skin infection):** This is true. While meningitis is the most common presentation, primary or secondary cutaneous cryptococcosis can occur, presenting as papules, pustules, or ulcerations. **High-Yield Clinical Pearls for NEET-PG:** * **Virulence Factor:** The **Polysaccharide capsule** (Glucuronoxylomannan) is the most important; it inhibits phagocytosis. * **Staining:** **India Ink** preparation shows a "halo" (negative staining). **Mucicarmine** stains the capsule red. * **Culture:** Grows on **Bird Seed Agar** (Niger Seed Agar) producing brown/black colonies due to **Phenoloxidase** activity (melanin production). * **Drug of Choice:** Induction with Amphotericin B + Flucytosine, followed by Fluconazole.

Q: About 90 days post-bone marrow transplant, a 55-year-old white woman began to complain of dry cough, shortness of breath, and chest pain. She was started on antibiotics and blood culture obtained at the time was negative and there was not improvement. A computed tomography (CT) scan of the lungs showed a halo of low attenuation around a nodular lesion. Analysis of lung biopsy was similar to methenamine silver-stained section below. What is the most likely diagnosis for this patient?

Aspergillosis. ***Aspergillosis*** - **Halo sign** on CT (low attenuation around nodular lesion) is **pathognomonic** for invasive pulmonary aspergillosis in immunocompromised patients post-bone marrow transplant. - **GMS stain** reveals characteristic **septate hyphae** with **acute-angle branching** (45°), typical of *Aspergillus* species. *Candidiasis* - Typically presents as **disseminated candidemia** or **oral thrush** rather than pulmonary nodules with halo sign in post-BMT patients. - **GMS stain** would show **pseudohyphae** and **budding yeast cells**, not septate hyphae with acute branching. *Histoplasmosis* - More common in **endemic areas** (Ohio/Mississippi river valleys) and typically causes **diffuse pulmonary infiltrates**, not nodular lesions with halo sign. - **GMS stain** reveals **small intracellular yeasts** within macrophages, not septate hyphae. *Mucormycosis* - Though seen in immunocompromised patients, typically causes **rhinocerebral** or **pulmonary** disease with **tissue necrosis** and black eschar. - **GMS stain** shows **non-septate hyphae** with **wide-angle branching** (90°), contrasting with Aspergillus morphology.

Q: Brown, spherical, septate bodies found in pus are diagnostic of which condition?

Chromomycosis. **Explanation:** The presence of **brown, spherical, thick-walled, septate bodies** (also known as **Sclerotic bodies**, **Medlar bodies**, or **Copper-penny bodies**) in pus or tissue sections is the pathognomonic hallmark of **Chromomycosis** (Chromoblastomycosis). These structures represent the vegetative fungal form and are naturally pigmented due to melanin in their cell walls (dematiaceous fungi). **Why the other options are incorrect:** * **Geotrichosis:** Caused by *Geotrichum candidum*, it typically shows rectangular arthroconidia and true hyphae, not pigmented spherical bodies. * **Mucormycosis:** Characterized by broad, **non-septate (coenocytic)**, ribbon-like hyphae with right-angle (90°) branching. * **Sporotrichosis:** Caused by *Sporothrix schenckii*, it typically presents as **cigar-shaped yeast** cells in tissue. The characteristic clinical finding is "sporotrichoid spread" (nodules along lymphatic drainage). **High-Yield Clinical Pearls for NEET-PG:** * **Causative Agents:** Most commonly *Fonsecaea pedrosoi* and *Phialophora verrucosa*. * **Clinical Presentation:** Usually occurs in barefoot agricultural workers following traumatic inoculation. It presents as slow-growing, **verrucous (warty) plaques** or cauliflower-like lesions, most commonly on the lower limbs. * **Diagnosis:** KOH mount of "black dots" on the lesion surface or biopsy reveals the characteristic **Sclerotic bodies**. * **Treatment:** Itraconazole is the drug of choice; surgical excision or cryotherapy may be used for small lesions.

Q: San Joaquin Valley fever is caused by which organism?

Coccidioides immitis. **Explanation:** **Coccidioides immitis** is the causative agent of **Coccidioidomycosis**, also known as **San Joaquin Valley fever** (or simply Valley fever). This fungal infection is endemic to the arid regions of the Southwestern United States (specifically the San Joaquin Valley in California) and Northern Mexico. It is a dimorphic fungus that exists as mold in the soil and transforms into **spherules containing endospores** within the host lungs. **Analysis of Options:** * **B. dermatitidis (Blastomycosis):** Known as "North American Blastomycosis" or "Gilchrist’s disease." It is endemic to the Ohio and Mississippi River valleys and is characterized by "Broad-Based Budding" yeast. * **Cryptococcus neoformans:** An opportunistic encapsulated yeast (not dimorphic) commonly associated with pigeon droppings. It is a leading cause of fungal meningitis in HIV/AIDS patients. * **H. capsulatum (Histoplasmosis):** Known as "Darling’s disease" or "Ohio Valley Fever." It is associated with bird or bat droppings (guano) and is characterized by small intracellular yeasts within macrophages. **High-Yield Clinical Pearls for NEET-PG:** * **Morphology:** *Coccidioides* is unique among dimorphic fungi; it forms **spherules** in tissue, not yeast. * **Transmission:** Inhalation of **arthroconidia** (infectious spores) from disturbed soil or during dust storms. * **Clinical Presentation:** Ranges from a self-limiting flu-like illness to severe pneumonia. A classic triad includes fever, joint pain (Desert Rheumatism), and **Erythema Nodosum**. * **Diagnosis:** Identification of thick-walled spherules filled with endospores on KOH mount or biopsy. Culture on Sabouraud Dextrose Agar (SDA) shows highly infectious arthroconidia.

Q: Gram stained periorbital exudates in severe panophthalmitis with cellulitis in an elderly diabetic shows irregular branching aseptate and broad hyphae. Which of the following is the most likely diagnosis?

Apophysomyces species. ### Explanation **Correct Answer: D. Apophysomyces species** The clinical presentation of severe panophthalmitis and cellulitis in an elderly diabetic patient, combined with the specific microscopic findings, points directly to **Mucormycosis**. **Why Apophysomyces is correct:** * **Microscopic Morphology:** The description of **"irregular branching, aseptate (coenocytic), and broad hyphae"** is the classic hallmark of the order Mucorales. * **Clinical Context:** Diabetics are highly predisposed to Rhino-oculo-cerebral mucormycosis (ROCM). * **Genus Identification:** While *Rhizopus* is the most common cause globally, *Apophysomyces elegans* is a significant cause of invasive mucormycosis in India, often following trauma or in immunocompromised states. Among the given options, it is the only member of the Mucorales family. **Why other options are incorrect:** * **A. Candida:** Shows budding yeast cells and **pseudohyphae** (constrictions at septa), not broad aseptate hyphae. * **B. Aspergillus:** Characterized by **septate** hyphae with regular, **dichotomous branching at acute angles** (45°). * **C. Penicillium:** Also features septate hyphae and characteristic "brush-like" conidiophores (Penicillus) in culture; it does not match the "broad aseptate" description. **High-Yield Clinical Pearls for NEET-PG:** * **Staining:** Mucorales are best visualized with **KOH mount** or silver stains (GMS/PAS). They often stain weakly on Gram stain but appear as "ghost-like" broad outlines. * **Risk Factors:** Diabetic Ketoacidosis (DKA) is the classic association because Mucorales thrive in acidic, iron-rich environments (using siderophores). * **Treatment:** The drug of choice is **Liposomal Amphotericin B**, along with aggressive surgical debridement. * **Key Distinction:** * *Mucor/Rhizopus:* Aseptate, wide-angle (90°) branching. * *Aspergillus:* Septate, acute-angle (45°) branching.

Q: Maltese cross formation is observed on polarizing microscopy in which of the following?

Cryptococcus neoformans. **Explanation:** The correct answer is **Cryptococcus neoformans**. **Why it is correct:** *Cryptococcus neoformans* is an encapsulated yeast. When clinical specimens (such as CSF or tissue sections) or cultures are viewed under **polarizing microscopy**, the thick polysaccharide capsule exhibits **birefringence**. This optical property results in the characteristic **"Maltese cross"** appearance (a cross-shaped light pattern). This is a high-yield diagnostic feature used to identify the fungus in histopathological sections, especially when stained with Gomori Methenamine Silver (GMS) or PAS. **Analysis of Incorrect Options:** * **Penicillium marneffei (Talaromyces marneffei):** This is a dimorphic fungus characterized by intracellular yeast cells with a central transverse septum (fission). It does not show a Maltese cross. * **Plasmodium falciparum:** This is a protozoan parasite. While it produces hemozoin pigment, it does not exhibit the Maltese cross pattern. (Note: *Babesia* species show a "Maltese cross" arrangement of four merozoites in RBCs, but this is a structural arrangement, not a polarizing microscopy finding). * **Candida albicans:** This yeast typically shows budding cells and pseudohyphae. Its cell wall does not produce a birefringent Maltese cross under polarization. **NEET-PG High-Yield Pearls:** 1. **Maltese Cross in Microbiology:** Seen in *Cryptococcus* (polarizing microscopy) and *Babesia* (tetrad arrangement on Giemsa stain). 2. **Maltese Cross in Pathology:** Seen in **Urinary lipids** (nephrotic syndrome), **Starch granules** (contaminants), and **Ethyl glycol poisoning** (calcium oxalate crystals). 3. **Cryptococcus Stains:** India Ink (negative staining for capsule), Mucicarmine (bright red capsule), and Fontana-Masson (detects melanin in the cell wall). 4. **Virulence Factor:** The polysaccharide capsule (GXM) is the primary virulence factor, inhibiting phagocytosis.

Question 1

Which of the following organisms is most likely responsible for this finding?

Accepted Answer

Candida albicans

Answer

Aspergillus fumigatus

Answer

Cryptococcus neoformans

Answer

Mucor species

Question 2

A diabetic patient presents with facial pain, black nasal eschar and eye pain following
corticosteroid therapy. What is the etiological agent?

Accepted Answer

Rhizopus

Answer

Candida tropicalis

Answer

Aspergillus fumigatus

Answer

Cryptococcus neoformans

Question 3

A patient presents with fever, headache, and neck stiffness suggestive of meningitis. CSF
examination is performed, and Nigrosin stain reveals encapsulated budding yeast cells. Which of
the following organisms is the most likely causative agent?

Accepted Answer

Cryptococcus neoformans

Answer

Aspergillus fumigatus

Answer

Pneumocystis jirovecii

Answer

Histoplasma capsulatum

Question 4

Which statement is false regarding Cryptococcus neoformans?

Accepted Answer

Urease negative

Answer

Grows at 5°C and 37°C

Answer

Has 4 serotypes

Answer

Causes superficial skin infection

Question 5

About 90 days post-bone marrow transplant, a 55-year-old white woman began to complain of dry cough, shortness of breath, and chest pain. She was started on antibiotics and blood culture obtained at the time was negative and there was not improvement. A computed tomography (CT) scan of the lungs showed a halo of low attenuation around a nodular lesion. Analysis of lung biopsy was similar to methenamine silver-stained section below. What is the most likely diagnosis for this patient?

Accepted Answer

Aspergillosis

Answer

Candidiasis

Answer

Histoplasmosis

Answer

Mucormycosis

Question 6

Brown, spherical, septate bodies found in pus are diagnostic of which condition?

Accepted Answer

Chromomycosis

Answer

Geotrichosis

Answer

Mucormycosis

Answer

Sporotrichosis

Question 7

San Joaquin Valley fever is caused by which organism?

Accepted Answer

Coccidioides immitis

Answer

B. dermatitidis

Answer

Cryptococcus neoformans

Answer

H. capsulatum

Question 8

Opportunistic lung infections in AIDS are most commonly caused by which of the following pathogens?

Accepted Answer

Pneumocystis jirovecii

Answer

Klebsiella pneumoniae

Answer

Mucor species

Answer

Mycoplasma pneumoniae

Question 9

Gram stained periorbital exudates in severe panophthalmitis with cellulitis in an elderly diabetic shows irregular branching aseptate and broad hyphae. Which of the following is the most likely diagnosis?

Accepted Answer

Apophysomyces species

Answer

Candida

Answer

Aspergillus

Answer

Pencillium

Question 10

Maltese cross formation is observed on polarizing microscopy in which of the following?

Accepted Answer

Cryptococcus neoformans

Answer

Penicillium marneffei

Answer

Plasmodium falciparum

Answer

Candida albicans

Mycology — MCQs

Mycology — MCQs

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